The present invention relates to a process and a device for determining in real time the behavior of a craft, in particular of an aircraft.
It is known that, for numerous applications pertaining to an aircraft, such as an airplane or a helicopter, in particular for piloted simulations, it is necessary to ascertain the behavior of the aircraft, that is say all its movements, throughout this aircraft""s simulated flight domain. To estimate this behavior, a modeling of the various movements to be considered is generally carried out. Two types of modeling may be used for this purpose: nonlinear modeling and linear modeling.
Nonlinear modeling, which makes it possible to describe the behavior of the aircraft by a nonlinear model using flight mechanics equations, is established from a knowledge of the forces which act on the aircraft. In this regard, it is known, for example, that the aerodynamic forces fluctuate with the square of the air speed or that a rotary wing of a helicopter gives rise to nonlinear inertial effects.
A nonlinear model represents reality very faithfully with a rigorous and complete description of the forces and moments which act on the aircraft. Moreover, it is valid throughout the aircraft""s flight domain.
However, nonlinear modeling such as this exhibits several drawbacks:
it is complex and difficult to implement;
it requires a very long duration of calculation; and
correction of the corresponding nonlinear model, which presupposes very good knowledge of the equations of the model and of their parameters so as to identify the influential parameters and to make provision for appropriate modifications, is very complex and difficult to implement.
On the other hand, linear modeling which makes it possible to describe the movements of an aircraft by a linear equation (usually a vector equation, for which a state representation is then employed) represents the states of the aircraft by very simple relations. The parameters of which these relations are composed are the dampings, the stabilities and the couplings of the aircraft, as well as the control sensitivities experienced directly by the pilot. These parameters can therefore be easily tailored with respect to the flight.
Linear modeling such as this is therefore simple and can be implemented and corrected speedily and easily.
However, it exhibits a considerable drawback. This linear modeling is valid only locally, about an equilibrium state. Its domain of validity is in principle limited:
in amplitude (one is constrained to move along a xe2x80x9ctangentxe2x80x9d to the point of equilibrium); and
in frequency (the number of natural modes that a linear model can reproduce is related directly to the dimension of its state vector.
Despite all its advantages, this linear modeling cannot therefore be used to estimate, at any instant and throughout the flight domain, the behavior of an aircraft.
The object of the present invention is to remedy these drawbacks. It relates to a process for determining in real time, easily and at reduced cost, the behavior of a craft, in particular of an aircraft, doing so throughout the domain of operation of this craft.
For this purpose, according to the invention, said process is noteworthy in that the following successive operations are carried out repetitively:
a) a vector xcex illustrating an equilibrium state is determined from a current linear model modeling the behavior of the craft;
b) the values at equilibrium of parameters of said linear model are determined from this vector xcex;
c) the dynamic component of the behavior of the craft is calculated from at least some of these values; and
d) this dynamic component is introduced into said linear model to obtain a new current linear model and to deduce the behavior of said craft therefrom.
Thus, by virtue of the invention, a linear model is used which exhibits numerous advantages (simplicity, speed of calculation, etc.), as stated above. Moreover, by virtue of its continual updating, this linear model can be used without restriction throughout the domain of operation (flight domain in the case of an aircraft) of the craft.
Moreover, said process according to the invention can be implemented for any type of craft (helicopter, airplane, automobile, rocket, missile, etc.) flying or otherwise.
Advantageously, the parameters of the linear model, whose values are determined in step b), are:
a state vector;
a control vector;
an observation vector;
a state matrix;
a control matrix; and
an observation matrix.
According to the invention, the values of said parameters are determined in step b):
xcex1) with the aid of a nonlinear model, this however being fairly unwieldy, since it is necessary to determine the values at each cycle; or
xcex2) with the aid of a pre-established database; or
xcex3) with the aid of relations, for example polynomial regressions which make it possible to define these parameters directly from the vector xcex, this corresponding to a simplified mode of deployment; or
xcex4) with the aid of a combination of at least two of the above methods xcex1), xcex2) and xcex3).
The database (used in the aforesaid method xcex2) can be updated at will without constraint (on the dimension of the vectors and matrices of which it is composed) other than the capacity of the computer used. According to the invention, this database can be established:
either with the aid of a nonlinear model;
or from measurements carried out during at least one movement of said craft. In the latter case, a model which is particularly faithful to reality is obtained.
The present invention also relates to a device for determining in real time the behavior of a craft, in particular of an aircraft, and capable of implementing the aforesaid process.
According to the invention, said device is noteworthy in that it comprises:
first means for determining, from a current linear model modeling the behavior of the craft, a vector xcex illustrating an equilibrium state;
second means connected to said first means, for determining, from this vector xcex, the values at equilibrium of parameters of said linear model;
third means connected to said second means, for calculating, from at least some of these values, the dynamic component of the behavior of the craft; and
fourth means connected to said first and third means, for introducing this dynamic component into said linear model so as to obtain a new current linear model and to deduce the behavior of said craft therefrom.